Big 3D printer (BigFDM)

TLDR:
I'm seeking an advice or two for large 3D printer build. Would the Duet 3 or Duet 2 be a good controller for a BigFDM 3D printer with 2x extruders, 1xNEMA 23 (2.8 A) and 2xNEMA 24 (4.2A) stepper motors + 4 bed heaters + Raspberry Pi 4 with display or would some other Duet controller be more suitable for the operation? The goal is to make this large 3D printer to be a "easy-to-use", reliable and upgradeable for our university's protolab where users (university students) might have near zero skills with 3D printers. Currently we have a couple of Prusa i3 MK3S printers in our protolab, so our background is fire-and-forget.

The long version:
I'm part of the team which is building a BigFDM 3D printer (the print area is 800 x 800 x 900 mm) for our university's protolab. Our protolab is open for all of our university students with wide ranging 3D print skill levels. So goal for new 3D printer is easy-to-use and reliable.

Our team are following the build instructions that can be found in the BigFDM's GitHub page, here https://github.com/fab-machines/BigFDM. The build consists of two Geeetech MK8 extruders (we might upgrade these in future), four 300 x 300 mm 220 V 750W bed heaters, one 2.8 A NEMA 23 (23HS22-2804S) and two 4.2 A NEMA 24 (24HS34-3008D) stepper motors. The controlling electronics are made in FabLab-style, Arduino Mega based board, TB6600 style stepper drivers and A4988 stepper drivers for extruders etc..

But I have some concerns that the BigFDM's original DIY control electronics are not as safe (mainly the fire hazard) and reliable for our protolab environment as some commercial controllers would be. Don't get me wrong, I do consider the original BigFDM DIY electronics to be a nice way to do all in a single lab. But my main goal is make sure that the electronics are reliable and easy to use, even after I or my team have left the building (as some of us are students which will some day graduate). Also we are looking for a controller which is tested, documented and safe to use in prints that take days to finish. (Or maybe our concern isn't the controller itself rather than extruders and bed heaters..)

For this reason I'm considering to use Duet 3 (or Duet 2) as controller because it seem to be able to drive these steppers directly, also it has some neat functionalities like a web interface (maybe we could monitor 3D printer remotely?), CAN-bus for upgrades, SBC support, many I/O ports...

So I'm looking for some advices/hints if this is at all possible with Duet controllers, or if there are some limitations I'm not aware and need to consider. I have read some of the forum posts regarding the large 3D printer projects and overall it seems doable. One concern though, we have some Prusa i3 MK3Ss, so I'm wondering how big step from Prusa-Marlin firmware to RepRapFirmware we would be taking?

pretty much limit you to the Duet3 or using external drivers with Duet2. 4 Bed heaters will likely require some external FET or SSR on both the Duet3 and Duet2. Other than that it should be pretty-straight-forward(tm)

There's no reason to not use a commercial PCB. Especially if your intent is to make a tool, not a project.

The NEMA24's seem odd to me, but only because NEMA23 is a more standard size... you can get motors in '23 size with a identical performance as those '24s.
There's also no reason why you couldn't use something like the Duex and use 2 motors to drive the Y axis (although I'm skeptical they need such a massive motor for the Y) which would remove the need for external steppers.

You can setup both RRF and Marlin based machines with Octoprint, which has more functionality than DWC, but requires an extra SBC and that work (but can do things like stream a webcam out to the internet).

The main reason to use the Duet boards is that they are using much more modern stepper drivers (quiet printers are good, especially when they are huge). The A4988 is antique trash and people should stop using them.

The main reason to use the RRF is that its a more modern and capable firmware than Marlin, with much better capabilities. Its worth becoming familiar with it now, rather than later. It opens up things like a more modern CPU that can actually push high step rates...

The jump from Prusa/Marlin to RRF... minor. RRF is much more pleasant to configure, other than that, on a conventional Cartesian FDM machine? Its minor.

And while those silicone heaters driven with SSR's are the right way to go, make sure you include some kind of thermal fuse. SSR's can and will fail on, and silicone heaters will melt if they get hot enough. A 200C thermal fuse attached to the bed is not a bad idea (or do the simulation and make sure the bed can't get to a dangerous temp).

After reading some documentation of the Duet 3 and Duet 2 (mainly Wifi and Maestro), I think we are going with Duet 3 board, even if it might be little overkill for the stepper motors. The main reason for this is that it is said in the BigFDM Github page Readme section that NEMA 24 is going to draw max. 4 A current (a single NEMA 24 is used for the Z axis). The Z axis might be somewhat "heavy" considering the weight of the bed plate, bed heaters and the print itself, so you would think it is going to draw a little bit higher current than in a "normal setup". And there is that fact we already have those stepper motors, so better to try to use them.

The webcam with stream support is also what we need and it seems we could do it with a Raspberry Pi 4 B, we could even use an old Android phone as a webcam). There are a couple of different ways to do the webcam stream, but the easiest solution seem to be motionwebcam server for the Raspberry Pi.

Also I noticed that BigFDM page recommends to use SSRs for this size bed heaters. With Duet 3 it seems that we would be able to drive these with the four IO pins using four SSR or just connect a single SSR's input to OUT0 and then connect these four bed heaters to the SSR.
As @theruttmeister said:

A 200C thermal fuse attached to the bed is not a bad idea.

Actually, this is a good idea, that would add some extra protection for the night prints! We will check this.

Funny enough, last weekend I talked with my neighbor who has Duet 2 Wifi in his CoreXY style 3D printer and he did say the Duets are quite easy to use after the configuration.

I hope we have the time to make a how-to documentation this summer, so I could put that somewhere here with the builds other users have made.

Also I noticed that BigFDM page recommends to use SSRs for this size bed heaters. With Duet 3 it seems that we would be able to drive these with the four IO pins using four SSR or just connect a single SSR's input to OUT0 and then connect these four bed heaters to the SSR.

when mains powered SSR is the way to go for the beds, you could also probably run 4 SSRs off the single output. that would allow you to later reconfigure to use 4 outputs to control quarters of the bed, as well as lower the load and potential need for cooling on each SSR.

(not sure how thermal expansion affects partially heated bed in practical terms, but there are at least on thread on here that deals with it for a large printer).